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Ultrasound of Peripheral Nerve & Muscle

Benefits of ultrasound imaging

Ultrasound offers a painless, harmless, dynamic, real-time examination, with superior spatial resolution. By ultrasound, healthy nerves appear as continuous bundles of neuronal fascicles separated from surrounding connective tissue. Some of the pathologic features encountered include breaks in the connective tissue, loss of fascicular architecture and swelling. Other identifiable pathological features include adjacent aneurysms, cysts and tumors.

Added value for entrapment neuropathies

For carpal tunnel syndrome, ultrasound has been shown to provide added value to other procedures, such as electromyography. Ultrasound is specific and sensitive for compression of the median nerve at the wrist. The test also can identify other structures that can complicate surgical procedures if not appreciated early, such as a persistent median artery within the carpal tunnel.

There is increasing evidence of ultrasound’s value in other peripheral nerve entrapment syndromes, particularly when electrodiagnostic localization is not possible. When evaluating the ulnar nerve at the elbow, abrupt narrowing of the nerve at the compression site and increased adjacent cross-sectional area are specific for entrapment. Examining the ulnar nerve within the ulnar groove with a flexed and extended elbow can also demonstrate subluxation of the nerve, suggesting increased risk of subsequent injury. Nerves of the lower extremity also can be successfully studied for evidence of injury or entrapment.

A useful adjunct to MRI in peripheral nerve disorders

Imaging techniques such as MRI offer a larger field of view and the opportunity to utilize intravenous contrast, but their value is counterbalanced by high cost and the extensive scan time needed to image a nerve along its entire course. Ultrasound can identify focal nerve enlargements (e.g., nerve tumors) and whether injured nerve severed after injury, for example, and can be useful as an initial localizing tool to guide a subsequent neuroimaging procedure.

High-resolution ultrasound is useful for imaging the peripheral nervous system and has been shown to be a valuable adjunct to EMG and other neuroimaging modalities.